It depends on your location. I almost lost one because she tried to cut through 2 Hoards. Its better to look at that map and decide for yourself. the farther you are from your the base, the more likely you are to lose them. Having outposts nearby also contribute to their survival.
Yes but becareful the scavenger's AI is not the greatest and they will b line it too home so if a horde or any other obsticle is in thier way they either better have good stats or you need to help them.
I haven't run into any problems with them running in to trouble on the way home but for those that have. Does it tell you if they run into a horde or need help or anything? or will they just die and you don't see them again. A little warning would be nice.
I've had some problems calling for scavengers over really long distances. The AI pathfinding thinks the location is always at the ranger station and they never go the the place I call for if the location is outside the small part of town my base is located at. Its very annoying.